Mixing and residence time distribution in melt screw extruders

Abstract The residence time distribution (RTD) functions were derived for screw extruders, based on the “parallel plate” and curved channel flow models. The results indicate a relatively narrow distribution, and they explain several characteristics of screw extruders. The strain distribution in the fluid across the channel was also derived. With the aid of these two functions an average strain of the fluid leaving the extruder was defined. The resulting weighted‐average total strain (WATS) provides a quantitative criterion to the “goodness of mixing” in extruders.